10 Java Common Mistakes beginners made

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Beginners don’t follow the rules: Creating objects only when it is necessary. Here is an example:

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public class Person {
    public boolean hasFollowedLeifeng(){
        Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        gmtCal.set(1950, Calendar.JANUARY, 1, 0, 0, 0);
        Date leifengStart = gmtCal.getTime();
        gmtCal.set(1983, Calendar.JANUARY, 1, 0, 0, 0);
        Date lefengEnd = gmtCal.getTime();
        return birthDate.compareTo(leifengStart) >= 0 && 
               birtheDate.compareTo(leifengEnd) < 0 ;
    }
}

public class Person {
    public boolean hasFollowedLeifeng(){
        Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        gmtCal.set(1950, Calendar.JANUARY, 1, 0, 0, 0);
        Date leifengStart = gmtCal.getTime();
        gmtCal.set(1983, Calendar.JANUARY, 1, 0, 0, 0);
        Date lefengEnd = gmtCal.getTime();
        return birthDate.compareTo(leifengStart) >= 0 && 
               birtheDate.compareTo(leifengEnd) < 0 ;
    }
}